Tobacco smoke filter

ABSTRACT

A tobacco smoke filter or filter element including a longitudinally extending core of tobacco smoke filtering material of perimeter 14 to 17 mm; and an additive release vessel fully enclosed within the core; wherein the filtering material is a filamentary material having a filament denier of 5.3 or greater and a total denier of 18,000 or less.

The present invention relates to tobacco smoke filters and filter elements, for example for smoking articles such as cigarettes.

The manufacture and use of cigarette filters containing a breakable capsule is well-known. On breakage by the smoker prior to, during, or after smoking, these capsules release liquid or substances contained therein—typically flavourants—that can in turn be transferred to the cigarette smoke whilst the cigarette is being smoked, or into the surrounding environment after the cigarette has been extinguished.

It is also known to provide cigarette filters in a variety of different circumferences, typically from around 25 mm to around 14 mm. These are known as ‘standard’, ‘slim’, ‘superslim’ and ‘microslim’ products as the filter circumference decreases within this range (e.g. from around 24.5 mm, to around 23 mm, to around 16-17 mm, to around 14-15 mm respectively). However, to date, there has been no commercial exploitation of capsule-bearing filters in the superslim (circumference around 16-17 mm) and micro-slim (circumference around 14-15 mm) formats. One of the issues is that the capsule tends to occupy a relatively higher proportion of the cross-sectional area of a superslim or microslim filter product, resulting in an unacceptably high pressure drop (because the smoke is channelled through a narrower conduit surround the capsule).

According to the present invention in a first aspect there is provided a tobacco smoke filter or filter element comprising a longitudinally extending (e.g. substantially cylindrical) core of tobacco smoke filtering material of perimeter (e.g. circumference) 14 to 17 mm (e.g. 16 to 17 mm); and an additive release vessel (e.g. a capsule) fully enclosed within the core; wherein the filtering material is a filamentary material (e.g. a filamentary filter tow) having a filament denier of 5.3 or greater and a total denier of 18,000 or less.

Preferably, the longitudinally extending core of tobacco smoke filtering material is a substantially cylindrical core of tobacco smoke filtering material.

Preferably, the longitudinally extending core of tobacco smoke filtering material is of circumference 16 to 17 mm (that is, the filter or filter element is a superslim filter or filter element).

The filter or filter element may further include a wrapper (e.g. paper, plugwrap) engaged around the longitudinally extending (e.g. substantially cylindrical) core. The wrapper may be a wrapper of paper, for example a wrapper of an air-permeable paper.

The additive release vessel (e.g. a capsule) is fully enclosed within the longitudinally extending (e.g. substantially cylindrical) core of tobacco smoke filtering material. This means that the additive release vessel (e.g. a capsule) is not visible (to the smoker) at the mouth or buccal end of the filter/filter element, or at the mouth end of a cigarette including a filter of this aspect of the invention, in use. Preferably at least one end of the longitudinally extending (e.g. substantially cylindrical) core of tobacco smoke filtering material has a uniform appearance. Preferably at least one end of the longitudinally extending (e.g. substantially cylindrical) core of tobacco smoke filtering material has a uniform appearance such that only the tobacco smoke filtering material is visible at that end of the core (e.g. such that other components such as additive, channels or similar are not visible at that end of the core). A uniform end appearance (e.g. an appearance such that only smoke filtering material is visible at that end of the core) may advantageously be pleasing to the smoker.

The tobacco smoke filtering material of the longitudinally extending core may be any filamentary material conventionally employed for tobacco smoke filter manufacture. The filtering material may be a natural or synthetic filamentary tow, e.g. of cotton or plastics such as polyethylene or polypropylene, or cellulose acetate filamentary tow. Preferably, the filtering material is filamentary cellulose acetate tow.

According to the present invention in an aspect there is provided a tobacco smoke filter or filter element comprising a longitudinally extending (e.g. substantially cylindrical) core of tobacco smoke filtering material of perimeter (e.g. circumference) 14 to 17 mm (e.g. 16 to 17 mm); and an additive release vessel (e.g. a capsule) fully enclosed within the core; wherein the tobacco smoke filtering material is (e.g. filamentary) cellulose acetate (e.g. cellulose acetate tow) having a filament denier of 5.3 or greater and a total denier of 18,000 or less.

Preferably, the longitudinally extending core of tobacco smoke filtering material is a substantially cylindrical core of tobacco smoke filtering material.

Preferably, the longitudinally extending core of tobacco smoke filtering material is of circumference 16 to 17 mm (that is, the filter or filter element is a superslim filter or filter element).

The filter or filter element may further include a wrapper (e.g. paper, plugwrap) engaged around the longitudinally extending (e.g. substantially cylindrical) core. The wrapper may be a wrapper of paper, for example a wrapper of an air-permeable paper.

The specification of a filamentary tobacco smoke filtering material (e.g. filter material tow) such as cellulose acetate is described in terms of the denier per filament (dpf); total denier; and the fibre cross-sectional shape. The filament denier is defined as the weight in grams of 9000 metres of a single filament; the total denier is then simply the dpf multiplied by the number of filaments in the tow. Thus, for example, a 5Y30,000 tow describes a material with a filament with a dpf of 5 grams per 9000 metres in the shape of a Y, comprising 6,000 filaments giving a total denier of 30,000 grams per 9000 metre length; a 5.2Y18,000 tow describes a material with a filament with a dpf of 5.2 grams per 9000 metres in the shape of a Y, comprising about 3,500 filaments giving a total denier of 18,000 grams per 9000 metre length; and a 6.8Y15,000 tow describes a material with a filament with a dpf of 6.8 grams per 9000 metres in the shape of a Y, comprising about 2200 filaments giving a total denier of 15,000 grams per 9000 metre length.

The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may having a filament denier of 5.3 or greater, for example 5.3 to 13, for example 5.3 to 12, for example 5.3 to 9, for example 5.4 to 8, for example 6 to 7. The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may have a filament denier of 5.3 to 7.9, 5.3 to 7.5, for example 6 to 7.5. The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may having a filament denier of 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9. In examples, the filamentary material may have a filament denier of 5.3 or greater, for example 5.4 or greater, for example 5.5 or greater, for example 5.6 or greater, for example 5.7 or greater, for example 5.8 or greater, for example 5.9 or greater, for example 6 or greater, for example 6.1 or greater, for example 6.2 or greater, for example 6.3 or greater, for example 6.4 or greater, for example 6.5 or greater.

The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may have a total denier of 9,000 to 18,000, for example 10,000 to 18,000, for example 12,000 to 17,000, for example 14,000 to 16,000. The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may have a total denier of 15,000 to 18,000, for example 15,100 to 18,000, for example 15,500 to 17,000, for example 15,500 to 16,000. The filamentary material (e.g. filamentary filter tow, cellulose acetate, cellulose acetate tow) may have a total denier of 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000. In examples, the filamentary material may have a total denier of 18,000 or less, for example 17,900 or less, for example 17,800 or less, for example 17,700 or less, for example 17,600 or less, for example 17,500 or less, for example 17,400 or less, for example 17,300 or less, for example 17,200 or less, for example 17,100 or less, for example 17,000 or less.

The filamentary material may be of any cross section (e.g. Y shaped cross section, X shaped cross section, circular cross section, the skilled person will appreciate that various cross sections are known in the art). Filamentary material of Y shaped cross section is preferred.

The additive release vessel may be a capsule, for example a frangible capsule. The (e.g. frangible) capsule may include additive in the form of a flavourant. The additive release vessel [(e.g. frangible) capsule] may contain one or more additives, for example a flavourant and/or a liquid, solid or other material, such as activated carbon, e.g. to aid smoke filtration. The use of additive containing capsules in filters is well known in the art.

The flavourant may be any flavourant known or suitable for use in a smoking article such as a cigarette, for example menthol, spearmint, peppermint, fenugreek, clove etc. Preferably the flavouring agent is or comprises menthol. The vessel (capsule) may comprise more than one flavouring agent (and may provide blends of different flavours, which may or may not include menthol).

The filter or filter element may include additive in the form of flavourant [e.g. in the the additive release vessel [(e.g. frangible) capsule], wherein the amount of additive (flavourant) is less than 35 mg (per filter/filter element). The filter or filter element may include additive in the form of flavourant [e.g. in the additive release vessel [(e.g. frangible) capsule], wherein the amount of additive (flavourant) is 5 to 30 mg, for example 7 to 25 mg, for example 10 to 25 mg, for example 10 to 20 mg (per filter/filter element).

The additive release vessel [(e.g. frangible) capsule] may be of width (when measured at its broadest point in a direction across the filter, that is perpendicular to the direction in which the longitudinally extending core extends) 2.0 to 4 mm, e.g. 2.5 to 3.9 mm, e.g. 3.0 to 3.8 mm, e.g. 3.2 to 3.7 mm, e.g. 3.5 mm. The additive release vessel [(e.g. frangible) capsule] may include less than 35 mg flavourant. The additive release vessel [(e.g. frangible) capsule] may include from 5 to 30 mg, for example 7 to 25 mg, for example 10 to 25 mg, for example 10 to 20 mg flavourant.

The filter or filter element may be of length 10 to 30 mm, e.g. 14 to 27 mm, e.g. 17 to 25 mm.

As set out in Example 1 below, the present applicants made superslim filters without capsules to determine minimum, maximum and optimum tow weights for the relevant filter dimensions, and then made corresponding filters with capsules, in order to assess the effect of the capsules on the pressure drop. Surprisingly, the applicants found that inclusion of a capsule in filter including a core of a filamentary filtering material (e.g. cellulose acetate tow) with a filament denier of 5.3 or greater (e.g. 6.8) and a total denier of 18,000 or less (e.g. 15,000) was associated with only a fairly small increase in pressure drop. This indicates that filamentary filter material (e.g. cellulose acetate tow) having filament denier of 5.3 or greater (e.g. 6.8) and a total denier of 18,000 or less (e.g. 15,000) may be particularly suited for use in capsule-containing superslim or microslim filters.

A filter element according to the invention may be used as a segment of a multi-segment slim filter, e.g. a dual, triple, other multiple filter. Such filters are well known in the art. If the filter element is used as or in a segment of a multi-segment filter, it may be used at (or in) the mouth or buccal end segment of the filter, or as (or in) any other segment of the filter. If the filter element is used as or in a segment of a multi-segment filter, the other segments may be, for example, wrapped or non-wrapper acetate segments; segments which include particulate or liquid additives such as activated carbon or flavours (e.g. active acetate filter segments, flavour thread filter segments); segments which comprise paper or nonwoven materials; other capsule-bearing segments etc. A filter element according to the invention may be used on its own e.g. as a single segment superslim or microslim filter (e.g. in the same way as a monoacetate filter).

Filters of the invention may be packaged and sold for use in Roll Your Own or Make Your Own smoking articles such as roll your own cigarettes. The filters may be packaged in a similar way to Pop-a-Tip™ filters for Roll-Your-Own (RYO) Smokers, which are well known and available from Filtrona Filters. Pop-a-Tip filters-type comprise a series of filters (filter tips) wrapped in a transparent film e.g. made of BOPP or cellophane. The filters are individually pushed (or ‘popped’) out of the transparent wrap by smokers of RYO products, who then use the filter when rolling their cigarette. According to the present invention in a further aspect there is provided a product rod comprising a plurality (e.g. two or more, e.g. 4-6) of individual tobacco smoke filters according to any aspect of the invention (or a plurality of individual tobacco smoke filters including filter elements according to any aspect of the invention) abutted end to end; and a (common) wrapper engaged around the plurality of filters or filter elements. The common wrapper may be a transparent material e.g. made of BOPP or cellophane.

In a filter cigarette according to the invention, a filter of the invention (or a filter which includes a filter element of the invention) is joined to a wrapped tobacco rod with one end of the filter towards the tobacco. The filter may be joined to the wrapped tobacco rod by ring tipping [which engages around just the adjacent ends of the (wrapped) filter and rod to leave much of the filter wrap exposed]. The filter may be joined by a full tipping overwrap (which engages around the full filter length and the adjacent end of the tobacco rod).

The filter, filter element or filter cigarette according to the invention may be ventilated by methods well known in the art, e.g. by use of a pre-perforated or air-permeable wrapper, and/or laser perforation of the wrapper and, if present, tipping overwrap. A ventilating full tipping overwrap may likewise be inherently air-permeable or provided with ventilation holes, and in ventilated products where both wrapper and tipping overwrap are present ventilation through the overwrap will usually (and preferably) be in register with that through the wrapper (e.g. plugwrap). Ventilation holes through the filter wrapper, or through a tipping overwrap, or through both simultaneously, may be made by laser perforation during filter or filter cigarette production, as is well known in the art.

According to the invention in a further aspect there is provided a multiple rod comprising a plurality (e.g. 2, 4, 6 etc.) of filters (or filter elements) as described above and/or herein integrally joined end-to-end in a mirror image relationship.

The present invention will now be illustrated with reference to the attached drawings in which:

FIG. 1 is a view of a tobacco smoke filter according to an example of the invention;

FIG. 2 is a view of the tobacco smoke filter of FIG. 1 with part cut away to show the interior of the filter;

FIG. 3 shows the capability curve for the 5.2Y18000 tow, as described in Example 1 below; and

FIG. 4 shows the capability curve for the 6.8Y15000 tow described in Example 1 below.

The filter 1 shown in FIG. 1 (and FIG. 2) includes a longitudinally extending substantially cylindrical core 2 of tobacco smoke filtering material of perimeter 16.8 mm and length 27 mm. (In actual fact the core 2 has circumference 16.8 mm, because the cylindrical core 2 is of circular cross-section.) The filtering material is a 6.8Y15,000 filamentary tow of filamentary cellulose acetate. Filter 1 also includes a wrapper 3 of plugwrap which is engaged around the longitudinally extending core 2 and held in place by a lapped and stuck seam, as is well known in the art.

Filter 1 also includes an additive release vessel in the form of a flavour containing frangible capsule 5 which is fully enclosed within the cylindrical core 2; the filtering material completely encloses the capsule. This is perhaps best seen in FIG. 2 (which shows a cutaway view of the filter and capsule) but the position of the capsule 5 within the core 2 is also shown in FIG. 1 by means of the dotted line 5 a. The additive release vessel is a spherical capsule 5 having diameter 3.5 mm which comprises a breakable outer shell 6 of gelatin or similar, which encloses menthol containing liquid 7. Such frangible or breakable spherical capsules 5, which include flavourant therein, and their methods of manufacture, are well known in the art.

Methods for making capsule containing filters are well known. It is well known to make longitudinally extending filter rods from filamentary filter materials such as cellulose acetate tow by drawing the cellulose acetate filamentary tow from a source, gathering the longitudinally advancing tow (e.g. by passing through a nozzle), and advancing the gathered/compressed tow through a garniture where the newly formed longitudinally extending rod of filtering material is wrapped in a plugwrap, and the plugwrap fixed in place by a lapped and stuck seam. The longitudinally advancing rod may be cut into individual filters, or, more usually, into multiple rod comprising a plurality (e.g. 2, 4, 6 etc.) of filters. This method may be adapted to make capsule containing filters by including a machine which inserts capsules (such machines are well known) into the process. In one such machine, (spherical) capsules 5 are held in a stack and fed consecutively into the longitudinally advancing filamentary cellulose acetate tow as it is gathered, so the advancing tow is gathered and compressed around capsules 5 as it passes through the nozzle and into the garniture. The resulting longitudinally advancing rod which includes capsules is cut into filters/rods in the usual manner.

The filter of FIG. 1 may be joined to a wrapped tobacco rod (not shown) with one end of the filter towards the tobacco, by methods well known in the art. The filter may be joined to the wrapped tobacco rod by ring tipping, which engages around just the adjacent ends of the wrapped filter 1 and rod to leave much of the wrapper 3 exposed, or joined by means of a full tipping overwrap which engages around the full length of the filter 1 and the adjacent end of the tobacco rod.

EXAMPLE 1 Trials for the Manufacture of Superslim Capsule Filters

Multiple length ‘mono’ filter rods were made by methods known in the art. Each multiple length filter rod comprised a longitudinally extending substantially cylindrical core of filamentary cellulose acetate of length 108 mm and a circumference of 16.8 mm. It will be appreciated that this rod is a multiple rod which may be cut down to four filters of length 27 mm (a so called “4 up” rod). Two different cellulose acetate filter tows were used—5.2Y18000 and 6.8Y15000. As is well-known, the first number (5.2 or 6.8) refers to the filament denier, Y refers to the filament cross-sectional shape and the second number (15000 or 18000) refers to the total denier of the tow.

The above mono filters/filter rods, without capsules, were assessed to determine the minimum, maximum and optimum tow weights for these filter dimensions—enabling the plot of a so-called ‘tow capability curve’. Such curves are well-known to those skilled in the art. Having determined these three points for the ‘mono’ rods (and also having confirmed that these values were consistent with those predicted by a standard modelling program ‘virtual tow selector’), corresponding rods with 4 evenly spaced capsules (spherical shape, diameter 3.5 mm) per 108 mm rod, one per filter in the rod, were made to assess the effect of the capsules on the pressure drop of the filters.

Tables 1 and 2 below show capability against pressure drop results for ‘mono’ filter rods and capsule containing filter rods including 5.2Y18000 tow (Table 1) and 6.8Y15000 tow (Table 2) following the assessment, and these data are also shown graphically in FIGS. 3 and 4.

The minimum point was determined as the tow weight which gave a 1 mm recess in the finished rod (i.e. the tow ‘sprang back’ to give a dished end to the finished filter/rod after cutting). The maximum point was determined by the tow weight which yielded a co-efficient of variation in pressure drop of around 6%—higher variability values are generally considered unacceptable. Tow weights were input into the virtual tow selector program to determine the ‘capability percentage’ shown in the Tables. The 5.2Y18000 tow item provided a capability range of −1 to 36%. The 6.8Y15000 tow item yielded a capability range of 0 to 70%.

TABLE 1 5.2Y18000 Tow Results Tow Mean Tip PD Circum- Weight PD PD Capa- Capsule Capability Rod ference (g/100 (mm/ CoV bility Increase Level Type (mm) rods) rod) (%) (%) (mm)* Low Mono 16.71 24.60 375.6 3.8 −1 Capsule 16.80 24.60 479.2 3.6 −1 33 Optimum Mono 16.85 25.88 399 3.4 9 Capsule 16.95 25.88 535 5.3 9 38 Maximum Mono 16.99 28.32 451 7.3 36 Capsule 17.17 28.32 584.8 6.4 36 27.2

TABLE 2 6.8Y15000 Tow Results Tow Mean Tip PD Circum- Weight PD PD Capa- Capsule Capability Rod ference (g/100 (mm/ CoV bility Increase Level Type (mm) rods) rod) (%) (%) (mm)* Low Mono 16.78 21.04 206.5 3.8 0 Capsule 16.81 21.04 267.7 4.3 0 15 Optimum Mono 16.83 23.92 288.3 5.3 34 Capsule 16.86 23.92 363.7 5.6 34 21 Maximum Mono 16.98 26.60 338.4 9.8 70 Capsule 17.17 26.60 429.8 8.8 70 18.9

Pressure drop is a key parameter in filter design. Decision criteria for available pressure drop range would be typically based on those data points that yielded a co-efficient of variation of 6% or less from the tow items. The available pressure drop range from the capsule filters using these tows was accordingly found to be 270-380 mm water gauge for 6.8Y15000 tow and 480-550 mm water gauge for 5.2Y18000 tow. Use of these tows outside these ranges, may yield poorly running or performing product (i.e. which is difficult to manufacture or has inferior performance). * Corrected for circumference differences and 4 tips per rod.

As expected, the addition of the capsule caused an increase in the pressure drop of the rod. The 5.2Y18000 tow saw an average pressure drop increase of 33 mm per tip (based on results for a 108 mm/4-up rod) whilst the average tip PD increase for the 6.8Y15000 tow was only 18 mm.

Thus, unexpectedly, the applicants found that inclusion of a capsule in filter including a core of a filamentary filtering material (e.g. cellulose acetate tow) with a filament denier of 5.3 or greater (e.g. 6.8) and a total denier of 18,000 or less (e.g. 15,000) was associated with only a fairly small increase in pressure drop. This indicates that filamentary filter material (e.g. cellulose acetate tow) having filament denier of 5.3 or greater (e.g. 6.8) and a total denier of 18,000 or less (e.g. 15,000) may be particularly suited for use in capsule-containing superslim or microslim filters. 

1. A tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of perimeter 14 to 17 mm; and an additive release vessel fully enclosed within the core; wherein the filtering material is a filamentary material having a filament denier of 5.3 or greater and a total denier of 18,000 or less.
 2. A tobacco smoke filter or filter element according to claim 1 wherein the longitudinally extending core of tobacco smoke filtering material is a substantially cylindrical core of tobacco smoke filtering material.
 3. A tobacco smoke filter or filter element according to claim 1 wherein the longitudinally extending core of tobacco smoke filtering material is of perimeter or circumference 16 to 17 mm.
 4. A tobacco smoke filter or filter element according to claim 1 further including a wrapper engaged around the longitudinally extending core.
 5. A tobacco smoke filter or filter element according to claim 1 wherein the filtering material is filamentary cellulose acetate tow.
 6. A tobacco smoke filter or filter element according to claim 1 wherein the filamentary material has a filament denier of 5.3 to 13, for example 5.3 to 9, for example 5.4 to 8, for example 6 to
 7. 7. A tobacco smoke filter or filter element according to claim 1 wherein the filamentary material has a total denier of 9,000 to 18,000, for example 10,000 to 18,000, for example 12,000 to 17,000, for example 14,000 to 16,000.
 8. A tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of perimeter 14 to 17 mm; and an additive release vessel fully enclosed within the core; wherein the tobacco smoke filtering material is cellulose acetate having a filament denier of 5.3 or greater and a total denier of 18,000 or less.
 9. A tobacco smoke filter or filter element according to claim 8 wherein the longitudinally extending core of tobacco smoke filtering material is a substantially cylindrical core of tobacco smoke filtering material.
 10. A tobacco smoke filter or filter element according to claim 8 wherein the longitudinally extending core of tobacco smoke filtering material is of perimeter or circumference 16 to 17 mm.
 11. A tobacco smoke filter or filter element according to claim 8 further including a wrapper engaged around the longitudinally extending core.
 12. A tobacco smoke filter or filter element according to claim 8 wherein the cellulose acetate has a filament denier of 5.3 to 13, for example 5.3 to 9, for example 5.4 to 8, for example 6 to
 7. 13. A tobacco smoke filter or filter element according to claim 8 wherein the cellulose acetate has a total denier of 9,000 to 18,000, for example 10,000 to 18,000, for example 12,000 to 17,000, for example 14,000 to 16,000.
 14. A tobacco smoke filter or filter element according to claim 1 wherein the additive release vessel is a capsule, for example a frangible capsule.
 15. A tobacco smoke filter or filter element according to claim 1 wherein the additive release vessel includes additive in the form of a flavourant.
 16. A tobacco smoke filter or filter element according to claim 1 wherein the additive release vessel is of width 2.0 to 4 mm, e.g. 3.2 to 3.7 mm, e.g. 3.5 mm.
 17. (canceled)
 18. A filter cigarette comprising a filter according to claim 1, joined to a wrapped tobacco rod with one end of the filter towards the tobacco.
 19. A multiple rod comprising a plurality of filters or filter elements according to claim 1 joined end-to-end.
 20. A product rod comprising a plurality of individual tobacco smoke filters according to claim 1, abutted end to end; and a wrapper engaged around the plurality of filters.
 21. A filter cigarette comprising a filter which includes a filter element according to claim 1, joined to a wrapped tobacco rod with one end of the filter towards the tobacco.
 22. A product rod comprising a plurality of individual tobacco smoke filters including filter elements according to claim 1, abutted end to end; and a wrapper engaged around the plurality of filters. 